Skip to main content

Full text of "The Cambridge Natural History"

126

THE SKULL  OF MARSUPIALS

the original statement of Owen was correct, at least in part.     It

is at most feebly developed (see Fig. 58, p. 118).

As   to  skeletal   characters, the  Marsupial   skull  has   on   the

whole   a   tendency   towards   a   permanent   separation   of   bones

usually   firmly   aukylosed.       Thus   the   orbitosphenoids   remain

distinct from the pre-
sphenoid. The palate is
largely fenestrated, a return
as it were—says Professor
Parker—to the Schizogna-
thous palate of the bird.
The mandible is inflected;
this familiar character of
the Marsupials goes back
to the earliest representa-
tives of the order in Meso-
zoic times (see p. 96); but
it is not absolutely uni-
versal, being absent from
the much weakened skull
of Tarsipes. On the other
hand, the inflection is nearly
as great in certain Insecti-
vores, in Otocyon, etc. The
malar always extends back
to form part of the glenoid

FM. 62. —Skull of Rock Wallaby• (Petroffaie cavity.    The shoulder girdle

peniGwata). (ventralview.; aCi, Alisplienoui;            **                                          .

l>as.oc, ba«i-ocelpital ; bos^h, basi-aphenoid ;   has   lost   the    large   COracoid

ex,oc-, ex-occipital ; //*, jugal ; max) maxilla ;

joal, palatine;  jpttr.oc,  parocoipital ;   p.max,

premaxiila; pr.sph, presphenoid ; pi, ptery-

goid ; s(ft squamosal ;  ty, tympanic.     (From

Parker ai

and Haswell's Zoology.)

of Monotremes ; this bone
has the vestigial character
that it possesses in other
Eutheria. The clavicle is
present except in the Peramelidae. A third trochanter upon
the femur seems to be never present.
The Marsupials cannot be regarded as an intermediate stage
in the origin of the Eutheria for a number of reasons. In the
first place, the nature of their teeth shows them to be degenerate
animals; one set, whether we regard it as the milk or permanent
dentition, has become vestigial. The recent discovery of a true
allatitoic placenta in Perameles removes one reason for regarding